Not Applicable
Not Applicable
The management of large skeletal defects continues to present a major challenge to orthopaedic surgeons, particularly when the problem arises in young patients in whom artificial devices and joint implants are likely to lead to early failure. Both cemented111,145 and uncemented60,75,139 devices have been shown to have significant and potential complications in young adults and children.
For example, there is a marked increase in the use of large frozen cortical bone allografts in limb-sparing procedures. These are used in the treatment of bone tumors19,26,44,48,77,104,105,107,112,146,159, for repair of massive bone loss due to traumatic injury69,99, in the treatment of avascular necrosis12, and, increasingly, in failed joint arthroplasties, where extensive bone loss due to osteolysis is commonly encountered47,56,76,109,125,130. Even though the overall success rate for massive cortical bone allografts, as measured by return to work and engagement in relatively normal activities without crutches or braces, is approximately 75-85%, only 50% of these patients have an entirely uncomplicated postoperative course. About a quarter of the total group require reoperations such as autologous grafting or replating for stress fractures4,5,32,103 or delayed unions43,70,71,103-105,127. Some patients require excision of the graft because of infection98,149,150, reimplantation, long-term bracing or, in some cases, amputation. These results clearly indicate that problems still exist with this procedure and that if the technique is to be more widely applied, it must be more extensively examined and materially improved. Therefore, development of a biologic alternative seems eminently worthwhile.
The present invention provides a biologic alternative to be used in conjunction with artificial devices and joint implants for the purpose of reducing immune responses and fostering the incorporation of graft bone, and, in particular, cortical bone allografts, into the graft recipient""s own bone. This approach can result in improvement of the clinical outcome of bone grafts and lower their complication rate.
In one aspect, the invention is directed to a composite biocompatible graft for cortical bone repair comprising a rigid biocompatible substratee having a porous biopolymer coating that is seeded with recipient periosteal cells. Preferably, the substrate material is a donor bone segment, e.g., a cortical bone allograft. In other embodiments, the allograft substrate material can be a resorbable precured bone cement, a molecularly reinforced interpenetrating network, a molded bioerodible polymer, or other similar materials.
The invention also relates to a grafting technique for promoting osteoinductivity and incorporation of a composite biocompatible bone graft in a lesion of a patient, comprising the steps of:
(a) producing a biocompatible graft substrate material;
producing, in vitro, cultured periosteal cells derived from said patient;
(b) coating said biocompatible graft substrate material with a porous biopolymer matrix;
(c) seeding said polymer matrix on said biocompatible graft substrate material with said cultured periosteal cells to form a composite biocompatible graft having an activated matrix; and
(d) implanting said composite biocompatible graft having said activated polymer matrix in said lesion.
Preferably, the polymer matrix is a polymer open-celled foam made from a bioerodible polymer such as poly(lactide-co-glycolide), which is also referred to as poly(lactic-co-glycolic) acid (PLGA; H[xe2x80x94OCHRxe2x80x94COxe2x80x94]OH, Rxe2x95x90H, CH3), and preferably a PLGA having a lactide to glycolide ratio of 50:50, but may also include any lactide:glycolide ratio from 0:100 (i.e., poly(glycolide)) to 100:0 (i.e., poly(lactide)). The lactide moiety may be d,l-lactide or l-lactide. Other bioerodible polymers that may be useful in the invention include polydioxanone; poly(caprolactone); polyanhydride; poly(orthoester); poly(ether-co-ester); polyamide; polylactone; poly (propylene fumarate), H[xe2x80x94Oxe2x80x94CH(CH3)xe2x80x94CH2xe2x80x94Oxe2x80x94COxe2x80x94CHxe2x95x90CHxe2x80x94COxe2x80x94]nOH; and combinations thereof. The thickness of the biopolymer foam coating ranges preferably from about 0.5 to about 1.5 millimeters, more preferably, from about 1 to about 2.5 millimeters. Adhesion of the polymer coating to the cortical bone graft is promoted by producing a surface roughness on the bone by grinding, laser ablation or other acceptable means.
The invention also relates to a biocompatible tissue transplant comprising a solid surface carrying a biopolymer coating to promote ingrowth of recipient tissues such as bone and blood vessels. The invention further relates to a tissue transplant of reduced immunogenicity comprising a solid surface carrying periosteal cells capable of regenerating autologous tissue.
The periosteal cells used in this invention are those that have been previously harvested either from the graft recipient or from allogenic or xenogenic donor sources. The periosteal cells are cultured in a matrix in media comprising inducers of osteogenesis selected from the group consisting of factors inducing bone formation, enzymes enhancing calcification, enzymes enhancing phosphorus deposition, vitamins, and prostaglandins.
The invention also encompasses a cortical bone allograft transplant for repair of bone defects comprising cells obtained by dissociating periosteal tissue, seeding periosteal cells on and in a biocompatible matrix suitable for repair of the defect, and culturing under culture conditions capable of inducing the periosteal cells to form new bone in the recipient of the transplant, thereby promoting incorporation in the transplant into the recipient""s own bone.